Telephone



(No Model.)

S. D. FIELD.

I TELEPHONE. No. 448,329. Patented Mar. 17, 1891.

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UNITED STATES PATENT OFFICE.

STEPHEN DUDLEY FIELD, OF STOOKBRIDGE, MASSACHUSETTS.

TELEPHONE.

SPECIFICATION forming part of Letters Patent No. 448,329, dated March 17, 1891.

A lication filed May 25, 1889. Serial No. 312,121. (No model.)

To all whom it may concern:

Be it known that I, STEPHEN DUDLEY FIELD, a citizen of the United S tates,residing at Stockbridge, in the county of Berkshire and State of Massachusetts, have invented certain new and useful Improvements in Electric Telephones; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to the construction of electric telephones, whether the same are to be used for transmitting or receiving articulate speech or vocal or other sounds proceeding from any source.

In my pending application, Serial No. 311,016, filed May 16, 1889, I have shown and described an electro-signal-receiving instrument of the polarized type, wherein the perm anent magnet is a practically-closed magnetic circuit and an open electromagnetic circuit, in which latter the vibrating tongue of the instrument is located. These two magnetic circuits are so arranged relatively that the currents flowing around the poles of the open electro-magnetic circuit will cause more or less lines of force to be deflected from the closed or practically closed magnetic circuit, owing to the peculiar reactionary effect of the currents in the coils of the electromagnets.

My present invention is based on similar principles and possesses peculiar advantages, as will be hereinafter referred to and the invention consists in the arrangement and combination of parts, substantially as hereinafter fully described, and particularly pointed out in the claims.

In the drawings, which form part of this specification, Figure l is a longitudinal section of one form of a hand-telephone constructed in accordance with my invention. Fig. 2 is a side elevation of the same, with the front or car piece in section. Fig. 3 is an end view with half of the earpiece cut away and the diaphragm broken off. Fig. 4 is a side elevation, partly sectional; and Fig. 5, an end elevation of a modified form of the instrument.

Referring now to Fig. l, I construct as follows: I take a permanent magnet 1, preferably of the compound type, made up of-a number of separately-magnetized steel bars, and" inclose this in a suitable handle or case 2, the poles of the system being respectively marked N and S. At the N pole Iplace a cylindrical iron armature 3, having flange 4., and this is attached to the magnet system by the core 5, whose projecting end (3 is screwed into the magnet 1. On the core 5 is mounted a helix 7. Across the face of the cylindrical box-armature 3 I place a diaphragm S, of magnetic material, and clamp this in position by means of a second or outer cylindrical iron box 9. The latter carries on its inner face a projecting tubular core 10, on which is mounted a helix 11, similar in all respects to the helix 7. The mouth 12 of the tubular core 10 is flared, as shown, for obvious purposes. The two helices 7 and 11 are so connected for circuiting purposes that the currents flowing through them will travel in opposite directions, as indicated by the arrows.

By the foregoing construction two paths are opened for the lines of force from the magnet-pole N, one by way of the walls of cases 3 and 9, with which the diaphragm 8 is in direct contact, and the other by way of the cores 5 and 10. The latter path or magnetic circuit is broken by the space between the cores 5 and 10, and in this space the dia-. phragm 8 is arranged for vibration. So far as concerns thecores 5 and l0,but very little polarity will normally be found between them in their adjacent ends, since the iron case 3 9 forms what may be termed a short circuit or magnetic shunt around the same,- and consequently the diaphragm 8 will not be attracted toward one any more than toward the other by the more influence of the permanent magnet.

Considering 110w that current impulses are passing through the coils 7 and 11. the action will be as follows: lVe will suppose that the current flows in coil 7 in such direction that it tends to end of core 5. Then a similar polarity will be developed in the front end of core 10. The

lines of force will tend to circulate through the two magnetic circuits formed by the diaphragm and the sides of the iron box. Those lines due to the magnetization of core 5 will tend to flow from the end of the core through the box 3 to the diaphragm, and through the induce S polarityat the front loo diaphragm to and. through the air-space between it and the core 5. These lines of force will be opposed in the air-space by the lines flowing through the air-space due to the permanent magnet N S; but the lines due to the coil 11 will proceed from the end of the core to the side of the box to the diaphragm to the air-space and back to the end of the core. These lines will be assisted in the air-space by the lines from the permanent magnet, but will oppose the flow of the latter through the box 9, and the lines from both sources will pass in multiple are through the diaphragm. The lines of force due to the permanent magnet will therefore follow the path through the box 3 to the diaphragm,through thediaphragm to core 10, and through core 10 to the south pole of the permanent magnet. It will therefore be seen that one core willbe strengthened and the otherwill be weakened by any given ourrent-impulse which circulates through their surrounding coils. The diaphragm will of course be attracted by the stronger polarity. The amount of this respective weakening and strengthening depends upon the current flowing. The result is a movement of the diaphragm 8 toward one or other of the cores with a force proportional to or dependent upon the strength of current used, and as the currents in the respective parallel coils 7 and 11 flow in opposite directions, their inductive effects largely serve to neutralize their magnetic lag, so that the latter is quite unaffected by the strength of current flowing. In all cases themovement of the diaphragm Sis exceedingly sharp and prompt whether the current used be very heavy or almost infinitely small.

The foregoing may be perhaps more clearly understood by assuming the presence of a mass of iron or imagining a phantom pole in front of the mouth-piece, as indicated by the dotted lines and polar letter.

In the form shown at Fig. at the same principles obtain but in this case I use both poles of the permanent magnet. The magnet 1 is here curved into a horseshoe, and each of its poles N S is provided with the iron cup or casing, respectively marked as before 3 and 9. i

The cases have their cavities facing each other, and between their edges is clamped the iron diaphragm 8. In the cases are fixed the inwardly-projecting cores 5 and 10, respectively, and upon these are mounted the coils 7 and 11, respectively, which are connected into the circuit, so that currents will flow in opposite directions in the'two. An ear-piece 15 is fixed to a suitable opening in one or both the iron cases, as shown.

Other modifications will readily occur to the skilled electrical constructer.

It will be understood that although the case 3 9 is shown of considerable thickness in the drawings this is done merely for the convenience of illustration. The material should be of the requisite thickness to carry the lines of force without great magnetic resistance,

and in many cases a sheet-metal box will be found to answer quite well.

Owing to the direct contact between the two cylindrical cases, there are but few lines of force between the ends of the cores 5 and 10 and the diaphragm, and in the normal state the latter is quite neutralthat is to say, the attraction toward either does not preponderate. The cores themselves, too, are in a practically neutral state, and therefore are excessively sensitiveto currents circulating in the coils around them. Supposing a current to be passing which tends to neutralize what few lines of force pass from the core 5 to the diaphragm, then this current will tend to increase the lines of force which pass through that position of the iron casing 3 enveloping the coil which surrounds said core. On the opposite side of the diaphragm, however, a reverse action takes place. Thelines of force between the core and diaphragm are increased and those in the iron casing are neutralized or diminished. An outward movement of the diaphragm will therefore occur with a force proportional to its production. It will thus be seen that the diaphragm lies in amagnetic shunt of high resistance around a normal magnetic short circuit, the path of the lines of force from the permanent magnet normally traveling from the short circuit by way of the box 3 9, but being deflected through a shunt formed by the diaphragm and one or other of the cores 5 10, accordingly as the current has one direction or the other. In fact, the currents which circulate through the coils around the cores 5 and 10 practically Vary the relative resistance of the shunt and the short circuit, increasing the resistance of the normal short circuit by interposing a magnetic resistance or opposition in a portion of its path and lowering the resistance of the shunt for the same reason. 7

Several important advantages arise from the application of the foregoing principles to a telephone. First, the diaphragm, being normally quite neutral, is free to respond fully and instantaneously to the most subtle electric currents; second, this condition of normal indifference permits the diaphragm to be set very much nearer the cores than usual, and as the magnetic attraction occurring is thereby much intensified the vibration is ampler and the sounds are louder; third, since the diaphragm is entirely freefrom the usual stress or magnetic strain, it can be made thicker or for a given thickness will have the maximumsensibility and will therefore respond to currents to whose influence under ordinary conditions it would be wholly inert; fourth, for the same reason where itis desired to have excessive sensibility I am enabled to have the diaphragm of extreme tenuity so as to readily respond to the smallest changes of current, and this may permit the use of a composite diaphragm composed of a non-metallic body IIO fifth, on account of the almosttotal absence of lines of force normally from the two cores the magnetic strength due to currents circulating in the coils will be substantially proportionate to the strength of such currents, and hence the line-currents can be greatly increased with a proportionate increase in the loudness of sounds given forth; sixth, the vibration of the diaphragm is positive in both directions-that is to say, each phase of one complete vibration is the result of an attraction as distinguished from an attraction and backward spring due to the elasticity of the diaphragm; seventh, the magnet, being al- Ways armed with a large mass of iron on its pole or poles, is always maintained at a maximum strength, and, eighth, the working resistance of the coils can be reduced to a minimum since their cores are so sensitive to inductive influence.

It will be apparent that while the usual practice is to polarize the core and diaphragm to the utmost possible extent, I proceed in directly opposite manner, and aim to have these parts as neutral as possible, though at the same time I may use a magnet of great strength without disturbing such desired neu trality.

I claim as my invention- 1. A telephone having its diaphragm supported between polar extensions of the two limbs of a magnet and magnetically connected at or near the rim, with an iron bridge connecting the poles of the magnet, each of the polar extensions being provided with a linecoil wound to develop like polarities at the confronting ends.

2. A telephone having its diaphragm in magnetic connection, with a short circuit between the poles of a permanent magnetic system and lying between two pole-pieces forming a high-resistance shunt around the short circuit, and line-coils for similarly polarizing the facing ends of the pole-pieces,

whereby the lines of force are diverted from the short circuit and forced through the shunt to act upon the diaphragm.

3. A telephone comprising a permanent magnet, a hollow iron box secured to the magnet, a diaphragm supported within the box, pole-pieces facing the diaphragm on opposite sides and in magnetic connection with the box, and reversely-wound coils 011 the polepieces.

4. A telephone comprising a permanent magnet, an iron box in magnetic connection 

